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Article

Direct Formation and Structural Characterization of Electride C12A7

1
Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 USA
2
Center for Materials Processing, University of Tennessee, Knoxville, TN 37996, USA
3
Department of Physics, Lovely Professional University, Phagwara 144401; India
*
Author to whom correspondence should be addressed.
Materials 2019, 12(1), 84; https://doi.org/10.3390/ma12010084
Received: 16 November 2018 / Revised: 7 December 2018 / Accepted: 21 December 2018 / Published: 27 December 2018
Ca12Al14O33 (C12A7 or Mayenite) is a material whose caged clathrate structure and occluded anionic species leads to significant functionality. The creation of occluded anionic vacancies leads to the injection of localized electrons at the center of the cage, converting the wide band gap insulator to a semi- or metallic conducting material. The conversion to the electride historically requires the synthesis of oxy-C12A7, consolidation, and then reduction to introduce anionic vacancies. This report develops and characterizes an electride formation procedure from three starting points: unconsolidated oxy-C12A7, heterogenous solid-state reactants (CaCO3 and Al2O3), and homogenous non-carbonaceous polymer assisted sol-gel reactants. Electride-C12A7 formation is observed in a vacuum furnace where the reactants are in direct contact with a carbon source. Process time and temperature-dependent structural characterization provides insight into the source of high temperature C12A7 stability, the mechanism of anionic vacancy formation, and the magnitude of ultimate conductivity that cannot be explained by current reduction theories. A new theory is presented where mixed O- and C-occupied cages lead to high temperature stability, oxidation of C species creates anionic vacancies, and an equilibrium between the reducing power of the electride-C12A7 and of the C species leads to the ultimate conductivity achieved by the process. This represents a shift in understanding of the carbonaceous reduction process and the first report of high purity electride-C12A7 formation from heterogenous solid-state reactants and homogenous non-carbonaceous polymer assisted sol-gel reactants. View Full-Text
Keywords: direct electride synthesis; C12A7; Ca12Al14O33; mayenite; electride structure; electride direct electride synthesis; C12A7; Ca12Al14O33; mayenite; electride structure; electride
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MDPI and ACS Style

Salasin, J.R.; Schwerzler, S.E.A.; Mukherjee, R.; Keffer, D.J.; Sickafus, K.E.; Rawn, C.J. Direct Formation and Structural Characterization of Electride C12A7. Materials 2019, 12, 84. https://doi.org/10.3390/ma12010084

AMA Style

Salasin JR, Schwerzler SEA, Mukherjee R, Keffer DJ, Sickafus KE, Rawn CJ. Direct Formation and Structural Characterization of Electride C12A7. Materials. 2019; 12(1):84. https://doi.org/10.3390/ma12010084

Chicago/Turabian Style

Salasin, J.R., S.E.A. Schwerzler, R. Mukherjee, D.J. Keffer, K.E. Sickafus, and C.J. Rawn 2019. "Direct Formation and Structural Characterization of Electride C12A7" Materials 12, no. 1: 84. https://doi.org/10.3390/ma12010084

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